The present invention relates to a method of preparing hexafluoroacetone by contacting, in the liquid phase, hexafluorothioacetone dimer with an aprotic solvent such as dimethyl sulfoxide or dimethylformamide in the presence of a catalytic amount of an alkali metal halide or organic sulfonic acid. The invention also relates to a method of preparing hexafluoroacetone by contacting, at low temperatures, hexafluoropropene with elemental sulfur and alkali metal halide in an aprotic solvent to produce hexafluorothioacetone dimer combined with reacting the dimer at elevated temperature with alkali metal fluoride in aprotic solvent to produce hexafluoroacetone.
Hexafluoroacetone is a known compound useful as an intermediate in the preparation of hexafluoropropanol and hexafluoroisobutylene, and for the preparation of compounds containing the (CF.sub.3).sub.2 C-- group.
W. J. Middleton et al. (J. Org. Chem., 30, 1384-1390 (1965)) disclose preparation of hexafluoroacetone by gas phase oxidation of hexafluorothioacetone dimer with nitric oxide, NO, at 650.degree. C., over quartz in a Vycor tube. However, this reference reports that nitric oxide does not react with hexafluorothioacetone dimer at low temperature, and that oxygen, which is also unreactive at lower temperatures, reacts with hexafluorothioacetone dimer at 650.degree. C. to give only high conversion thereof into carbonyl fluoride and sulfur dioxide, but no hexafluoroacetone.
U.S. Pat. Nos. 3,164,637 and 3,257,457 (L. G. Anello et al.) disclose preparation of hexafluoroacetone by high temperature, gas phase fluorination of hexachloroacetone with HF in the presence of a chromium catalyst.
U.S. Patent Application Ser. No. 238,920 filed Feb. 17, 1981 (L. G. Anello et al.) discloses a process for preparing hexafluoroacetone by contacting, in the liquid phase, hexafluorothioacetone dimer with a gaseous oxidant such as O.sub.2 in the presence of a catalytic amount of an alkali metal halide and an aprotic solvent such as dimethylformamide.
U.S. Patent Application Ser. No. 217,943 filed Dec. 18, 1980 (L. G. Anello et al.) discloses a process for preparing hexafluoroacetone by liquid phase reaction of hexafluorothioacetone dimer in an aprotic solvent containing alkali metal fluoride, at elevated temperature with selected metallic and non-metallic oxides.
U.S. Patent Application Ser. No. 216,035, filed Dec. 15, 1980 (L. G. Anello et al.) discloses a process for preparing hexafluoroacetone dimer by reacting hexafluoropropene with elemental sulfur and an alkali metal fluoride such as KF in an aprotic solvent such as dimethylformamide at temperatures between 25.degree. and 100.degree. C. However, the formation of hexafluoroacetone is not suggested or disclosed.
U.S. Pat. No. 4,057,584 (T. Touzuka et al.) discloses preparation of hexafluoroacetone by gas phase oxidation of perfluoropropene with oxygen over a fluorinated alumina catalyst.
These prior art preparations operate in the gas phase, employ high temperature, special equipment, gaseous oxidants, metallic and non-metallic oxide oxidants and specially treated catalysts.
In the presence of fluoride ion, hexafluorothioacetone dimer in dimethylformamide is in equilibrium with monomeric hexafluorothioacetone (T. Kitazume et al. Chemistry Letters, 267 (1973)).
Accordingly, there is a need for an economical process for the preparation of hexafluoroacetone which operates without special equipment, added oxidants or expensive catalysts.
It is an object of the present invention to provide a process for a liquid phase preparation of hexafluoroacetone without added oxidants or catalysts. This and other objects and advantages of the present invention will become obvious from the following description.